A research report submitted to the Faculty of Science in partial fulfillment of the requirements for the degree of Master of Science, 2016. / South African gold mines are associated with the generation of a lot of mine waste in
the form of milled rock (tailings). Tailings contain the mineral pyrite which, when exposed to air and water, cause acid mine drainage (AMD). Due to the large environmental impact
(footprint and scale) ofthe tailings storage facilities (TSFs) on soils and groundwater, there has been much research done in phytoremediation. Some plants, such as Eucalyptus, used in this method are able to control seepage by using their extensive roots but this may inadvertently extract some contaminants from the water and accumulate them in the above ground parts of the tree. Upon harvesting of these plants, there is the potential for them to be used as biofuel for the generation of bioenergy, and by industry or the public as timber/construction wood, firewood, charcoal, generation of electricity, etc. In this study, three species of Eucalyptus trees grown by the University of the Witwatersrand in three site-species trials on AMD were evaluated for their concentrations of elements in leaves, bark, branches/twigs and stem wood, in order to determine the safety of the biomass for fuel, and the potential for environmental pollution (dissemination of metals) that could be caused by combustion. The study focused on Eucalyptus camaldulensis, E. grandis x camaldulensis hybrid and E. dunnii trees grown for eight years in three different trial sites, with one trial ("Mispah") situated at AngloGold Ashanti's Vaal River Mining Operations (VR, near Orkney - Klerksdorp) and two trial("Madala", "Red Soil") situated at the West Wits Mining Operations (WW, near Carletonville). The sites were typical of soils on the mine properties (WW Madala: Clovelly, WW Red Soil: Hutton, VR Mispah: Hutton and Mispah), and impacted by seepage from adjacent TSFs. Three entire above-ground trees were harvested per species (three trees per site, nine in total), weighed fresh and after drying. Samples of leaves, bark, twig/small branches, and main stem wood were analysed for their elemental contents; alongside a Certified Reference Material (CRM) (Orchard Leaves no. 1571); using Leco CNS analyser, Inductively Coupled PlasmaOptical Emission Spectroscopy (ICP-OES) and Inductively Coupled Plasma-Mass Spectroscopy (ICP-MS) to determine the concentrations of major and trace elements such as Aluminium (AI), Barium (Ba), Calcium (Ca), Iron (Fe), Potassium (K), Magnesium (Mg), Manganese (Mn), Sodium (Na), Nickel (Ni), Phosphorus (P), Sulphur (S), Strontium (Sr), Titanium (Ti), Zinc (Zn), Vanadium (V), Chromium (Cr), Cobalt (Co), Copper (Cu), Arsenic (As), Gold (Au), Mercury (Hg), Lead (Pb), Uranium (U), carbon (C) and ash content. The CRM was used to validate the two analytical methods. There was variation in the concentrations of nutrients measured. There were no significant differences noted in the metallloids concentrations between all the Eucalyptus 11\ species studied (p>O.05). Variation between sites could not be determined as there were no replicates available to perform the comparison. The World Health Organisation (WHO) maximum permissible level (MPL) in plants for arsenic (As) is 1 mg/kg. The MPL was exceeded in all tissues of all three Eucalyptus species studied. Arsenic concentrations of 5.09, 4.36 and 5.48 mg/kg were found in the wood of E. camaldulensis, E. grandis x camaldulensis and E. dunnii respectively. A risk assessment performed found that there was no evidence that
there will be adverse effects caused by supplying fuelwood from these contaminated
Eucalyptus trees. Even though high arsenic concentrations were recorded in this study, if the wood is used as fertilizer in a vegetable bed, the transfer of the arsenic to the common
vegetables is below the daily oral reference dose. The general trend in the concentration of metals and metalloids in different plant tissues was in the order of leaves > bark >
branches/twigs > wood. The results of the biomass exposure assessment showed that the
exposure through use of the ash as fertiliser was lower than the oral reference dose for Mn, Fe, Ba and As. The biomass risk assessment showed that the best-performing tree, in terms of wood production on AMO, was the E. camaldulensis. The risk of other metallioids was not evaluated as there was no good agreement between the results recorded with those certified of the CRM. It is suspected that the CRM used was old. / AC2016
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/21591 |
| Date | January 2016 |
| Creators | Mosito, Nosipho Sylvia Vanessa |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | Online resource (xvi, 123 leaves), application/pdf |
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